= Cumulative coherence bound for restricted isometry
{title2=$\delta_s\le\mu_1(s-1)\le(s-1)\mu$}
For normalized columns and $1\le s\le N$, the <restricted isometry constant> is bounded by the <cumulative coherence> at $s-1$. A restricted <Gram matrix> has diagonal one and every off-diagonal row sum at most $\mu_1(s-1)$. The <Gershgorin circle theorem> and the <finite-dimensional spectral theorem> bound its <eigenvalues> between $1-\mu_1(s-1)$ and $1+\mu_1(s-1)$. At $s=1$ the distortion is zero, and at $s=2$ it is exactly the <mutual coherence>.
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